European patent No. 2 424 270 B1 discloses a loudspeaker which comprises an enclosure and a dynamic driver mounted in the enclosure. The enclosure is filled with a gas adsorbing zeolite material. Filling the enclosure with the gas adsorbing zeolite material results in an apparent virtual enlargement of the volume defined by the enclosure, increasing the effective volume of the enclosure. The gas adsorbing zeolite material comprises grains having an average grain size in a range between 0.2 and 0.9 mm and having a plurality of zeolite particles adhered together by means of a binder. The zeolite particles comprise pores and have a silicon to aluminum mass ratio of at least 200.